Semiconductor processing frequently involves etching of silicon-oxide-containing materials, such as, for example, silicon dioxide, borophosphosilicate glass (BPSG), etc. Semiconductor processing also frequently involves patterning etched materials with organic photoresist. masking materials. Organic photoresist materials can be either positive or negative photoresists, and can include, for example, novolac and cyclized synthetic rubber resin. A difficulty which can occur in etching silicon-oxide-containing materials results from limited selectivity of present etch methods for silicon-oxide-containing materials relative to organic masking materials. Such difficulty is described with reference to FIGS. 1-3.
Referring first to FIG. 1, a semiconductor wafer fragment 10 is illustrated. Wafer fragment 10 comprises a substrate 12 having a silicon-oxide-containing layer 14 thereover. Substrate 12 can comprise, for example, monocrystalline silicon lightly-doped with a p-type background dopant. To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Layer 14 can comprise, for example, silicon dioxide; can consist essentially of silicon dioxide, or can consist of silicon dioxide. Also layer 14 can comprise a doped silicon oxide, such as, for example, BPSG.
A patterned masking layer 16 is shown formed over silicon-oxide-containing layer 14. Masking layer 16 can comprise, for example, an organic photoresist material, and can be patterned by photolithographic processing.
Referring to FIG. 2, wafer fragment 10 is subjected to etching conditions which etch into silicon-oxide-containing material 14 to form an opening 18 extending therein. A suitable etch for silicon-oxide-containing material 14 is a plasma etch utilizing one or more of CF4, C2F6, H2, C3F8, and CHF3. FIG. 2 shows a thickness of masking layer 16 reduced during the etching of oxide layer 14. Such reduction in thickness occurs due to non-selectivity of the etch conditions for oxide material 14 relative to masking material 16. Generally, the etching conditions will have some selectivity for oxide layer 14, in that the material of oxide layer 14 will etch faster than will the material of organic masking layer 16. However, the selectivity is not absolute, and accordingly some of the organic material of layer 16 etches during the etching of the silicon oxide of layer 14.
Referring to FIG. 3, wafer fragment 10 is shown after continued etching of layer 14. Such continued etching has removed layer 16 (FIG. 2) from over layer 14. Such removal of layer 16 can be problematic in further processing steps.
It would be desirable to develop alternative methods for etching silicon-oxide-containing materials with enhanced selectivity for the silicon-oxide-containing materials relative to organic materials.